Ferric chloride compositions are extensively used commercially such as to etch various metals including steel, copper and aluminum.
For example, the etching of steel employing ferric chloride solutions is important in the manufacture of stainless steel printbands for impact printers and for integrated circuit chip carriers.
The activity of ferric chloride compositions diminishes over a period of time of use until it reaches a point where etching with the composition is no longer satisfactory. The decay or diminishing of activity is due to the reduction of the active ferric ion to the relatively inactive ferrous ion caused by the etching reaction itself. As the etch rate decreases, the amount of metal removed per unit time likewise decreases and, therefore, the etch process through put must then suffer. However, frequent dumping of the etch bath becomes a problem since it leads to large volumes of waste products that must be treated before being converted to a waste sludge. The treatment of the waste products is a relatively costly matter; and when etching stainless steel, the waste sludge generated is classified "hazardous" due to the presence of chromium in the stainless steel and thus the sludge. The hazardous waste sludge produced requires special handling and controls for proper disposal thereby further escallating costs.
There have been various suggestions to chemically regenerate ferric chloride solutions. Such suggestions have included relatively highly reactive, potentially explosive, and/or toxic chemical oxidizers such as sodium chlorate, hydrogen peroxide, ozone and chlorine. However, these methods are not desirable in view of safety and environmental concerns. In addition, there have been certain suggestions to regenerate ferric chloride solutions by aerating or oxygenating. However, the suggested procedures tend to be relatively slow and do not adequately keep up with the rate of formation of ferrous ion during high volume etching procedures.
More recently, there have been suggestions to employ electrolytic regeneration of certain ferric chloride compositions. However, the processes suggested are not entirely satisfactory from a standpoint of efficiency and safeness. Moreover, such processes are relatively expensive and costly to operate, and many of the suggested processes for electrolytic regeneration result in the generation of a significant amount of chlorine gas at the anode.